Implement an emergency cleanup handler registration mechanism to allow modules to clean themselves before application gets killed.

Flush PCAP contents just before killing the application.

lib/include/srsran/common/emergency_handlers.h

@@ -0,0 +1,25 @@
+/**
+ *
+ * \section COPYRIGHT
+ *
+ * Copyright 2013-2021 Software Radio Systems Limited
+ *
+ * By using this file, you agree to the terms and conditions set
+ * forth in the LICENSE file which can be found at the top level of
+ * the distribution.
+ *
+ */
+
+#ifndef SRSRAN_EMERGENCY_HANDLERS_H
+#define SRSRAN_EMERGENCY_HANDLERS_H
+
+using emergency_cleanup_callback = void (*)(void*);
+
+// Add a cleanup function to be called when a kill signal is about to be delivered to the process. The handler may
+// optionally pass a pointer to identify what instance of the handler is being called.
+void add_emergency_cleanup_handler(emergency_cleanup_callback callback, void* data);
+
+// Executes all registered emergency cleanup handlers.
+void execute_emergency_cleanup_handlers();
+
+#endif // SRSRAN_EMERGENCY_HANDLERS_H

lib/include/srsran/common/mac_pcap_base.h

@@ -28,6 +28,10 @@ class mac_pcap_base : protected srsran::thread
 {
 public:
   mac_pcap_base();
+
+  mac_pcap_base(const mac_pcap_base& other) = delete;
+  mac_pcap_base& operator=(const mac_pcap_base& other) = delete;
+
   ~mac_pcap_base();
   void             enable(bool enable);
   virtual uint32_t close() = 0;

lib/include/srsran/common/s1ap_pcap.h

@@ -21,7 +21,10 @@ namespace srsran {
 class s1ap_pcap
 {
 public:
-  s1ap_pcap() = default;
+  s1ap_pcap();
+  s1ap_pcap(const s1ap_pcap& other) = delete;
+  s1ap_pcap& operator=(const s1ap_pcap& other) = delete;
+
   void enable();
   void open(const char* filename_);
   void close();

lib/include/srsran/common/signal_handler.h

@@ -18,6 +18,7 @@
 #ifndef SRSRAN_SIGNAL_HANDLER_H
 #define SRSRAN_SIGNAL_HANDLER_H
 
+#include "srsran/common/emergency_handlers.h"
 #include "srsran/srslog/sink.h"
 #include "srsran/srslog/srslog.h"
 #include <signal.h>
@@ -41,11 +42,12 @@ static void srsran_signal_handler(int signal)
     case SIGALRM:
       fprintf(stderr, "Couldn't stop after %ds. Forcing exit.\n", SRSRAN_TERM_TIMEOUT_S);
       srslog::flush();
-      //:TODO: refactor the sighandler, should not depend on log utilities
+      //: TODO: refactor the sighandler, should not depend on log utilities
       if (log_sink) {
         log_sink->flush();
       }
       srsran_dft_exit();
+      execute_emergency_cleanup_handlers();
       raise(SIGKILL);
     default:
       // all other registered signals try to stop the app gracefully

lib/src/common/CMakeLists.txt

@@ -28,6 +28,7 @@ set(SOURCES arch_select.cc
             rlc_pcap.cc
             s1ap_pcap.cc
             security.cc
+            emergency_handlers.cc
             standard_streams.cc
             thread_pool.cc
             threads.c

lib/src/common/emergency_handlers.cc

@@ -0,0 +1,59 @@
+/**
+ *
+ * \section COPYRIGHT
+ *
+ * Copyright 2013-2021 Software Radio Systems Limited
+ *
+ * By using this file, you agree to the terms and conditions set
+ * forth in the LICENSE file which can be found at the top level of
+ * the distribution.
+ *
+ */
+
+#include "srsran/common/emergency_handlers.h"
+#include "srsran/support/srsran_assert.h"
+
+namespace {
+
+/// Holds the callback function pointer and the associated user provided data pointer.
+struct handler_instance {
+  std::atomic<void*>                      data{};
+  std::atomic<emergency_cleanup_callback> callback{};
+};
+
+} // namespace
+
+// Handlers are added in a thread safe manner without using locks to avoid possible issues if a signal is emitted while
+// modifying the callback array.
+static constexpr unsigned    max_handlers = 12;
+static handler_instance      registered_handlers[max_handlers];
+static std::atomic<unsigned> num_handlers;
+
+void add_emergency_cleanup_handler(emergency_cleanup_callback callback, void* data)
+{
+  // Reserve a slot in the array.
+  auto pos = num_handlers.fetch_add(1);
+
+  // Check if we have space in the array.
+  if (pos >= max_handlers) {
+    srsran_assert(0, "Exceeded the emergency cleanup handler registered limit");
+    return;
+  }
+
+  // Order is important here: write last the callback member as it is used to signal that the handler is valid when
+  // reading the array.
+  registered_handlers[pos].data.store(data);
+  registered_handlers[pos].callback.store(callback);
+}
+
+void execute_emergency_cleanup_handlers()
+{
+  for (unsigned i = 0, e = num_handlers; i != e; ++i) {
+    auto callback = registered_handlers[i].callback.load();
+    // Test the validity of the callback as it may have not been written yet into the array even if num_callbacks has
+    // been updated.
+    if (callback) {
+      callback(registered_handlers[i].data.load());
+    }
+  }
+}

lib/src/common/mac_pcap_base.cc

@@ -11,13 +11,23 @@
  */
 
 #include "srsran/common/mac_pcap_base.h"
+#include "srsran/common/emergency_handlers.h"
 #include "srsran/config.h"
 #include "srsran/phy/common/phy_common.h"
 #include <stdint.h>
 
 namespace srsran {
 
-mac_pcap_base::mac_pcap_base() : logger(srslog::fetch_basic_logger("MAC")), thread("PCAP_WRITER_MAC") {}
+/// Try to flush the contents of the pcap class before the application is killed.
+static void emergency_cleanup_handler(void* data)
+{
+  reinterpret_cast<mac_pcap_base*>(data)->close();
+}
+
+mac_pcap_base::mac_pcap_base() : logger(srslog::fetch_basic_logger("MAC")), thread("PCAP_WRITER_MAC")
+{
+  add_emergency_cleanup_handler(emergency_cleanup_handler, this);
+}
 
 mac_pcap_base::~mac_pcap_base() {}
 

lib/src/common/s1ap_pcap.cc

@@ -11,12 +11,24 @@
  */
 
 #include "srsran/common/s1ap_pcap.h"
+#include "srsran/common/emergency_handlers.h"
 #include "srsran/common/pcap.h"
 #include "srsran/srsran.h"
 #include <stdint.h>
 
 namespace srsran {
 
+/// Try to flush the contents of the pcap class before the application is killed.
+static void emergency_cleanup_handler(void* data)
+{
+  reinterpret_cast<s1ap_pcap*>(data)->close();
+}
+
+s1ap_pcap::s1ap_pcap()
+{
+  add_emergency_cleanup_handler(emergency_cleanup_handler, this);
+}
+
 void s1ap_pcap::enable()
 {
   enable_write = true;
@@ -29,6 +41,9 @@ void s1ap_pcap::open(const char* filename_)
 }
 void s1ap_pcap::close()
 {
+  if (!enable_write) {
+    return;
+  }
   fprintf(stdout, "Saving S1AP PCAP file (DLT=%d) to %s\n", S1AP_LTE_DLT, filename.c_str());
   DLT_PCAP_Close(pcap_file);
 }